/* zran.c -- example of zlib/gzip stream indexing and random access
 * Copyright (C) 2005 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
   Version 1.0  29 May 2005  Mark Adler */

/* Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary()
   for random access of a compressed file.  A file containing a zlib or gzip
   stream is provided on the command line.  The compressed stream is decoded in
   its entirety, and an index built with access points about every SPAN bytes
   in the uncompressed output.  The compressed file is left open, and can then
   be read randomly, having to decompress on the average SPAN/2 uncompressed
   bytes before getting to the desired block of data.

   An access point can be created at the start of any deflate block, by saving
   the starting file offset and bit of that block, and the 32K bytes of
   uncompressed data that precede that block.  Also the uncompressed offset of
   that block is saved to provide a referece for locating a desired starting
   point in the uncompressed stream->  build_index() works by decompressing the
   input zlib or gzip stream a block at a time, and at the end of each block
   deciding if enough uncompressed data has gone by to justify the creation of
   a new access point.  If so, that point is saved in a data structure that
   grows as needed to accommodate the points.

   To use the index, an offset in the uncompressed data is provided, for which
   the latest accees point at or preceding that offset is located in the index.
   The input file is positioned to the specified location in the index, and if
   necessary the first few bits of the compressed data is read from the file.
   inflate is initialized with those bits and the 32K of uncompressed data, and
   the decompression then proceeds until the desired offset in the file is
   reached.  Then the decompression continues to read the desired uncompressed
   data from the file.

   Another approach would be to generate the index on demand.  In that case,
   requests for random access reads from the compressed data would try to use
   the index, but if a read far enough past the end of the index is required,
   then further index entries would be generated and added.

   There is some fair bit of overhead to starting inflation for the random
   access, mainly copying the 32K byte dictionary.  So if small pieces of the
   file are being accessed, it would make sense to implement a cache to hold
   some lookahead and avoid many calls to extract() for small lengths.

   Another way to build an index would be to use inflateCopy().  That would
   not be constrained to have access points at block boundaries, but requires
   more memory per access point, and also cannot be saved to file due to the
   use of pointers in the state.  The approach here allows for storage of the
   index in a file.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "zlib.h"
#include <sys/types.h>
#include <sys/stat.h>
#include <assert.h>
#include "libzran.h"

static void zran_file_cleanup(struct zran_file *zf, int flags);
static int zran_inflate_open(struct zran_file *zf, int wbits);
static int zran_deflate_open(struct zran_file *zf, int level);
static void zran_index_cleanup(struct zran *zran, int flags);
static int zran_index_open(struct zran *zran);
static struct point *zran_index_load_point(struct zran *zran);
static void zran_index_next_point(struct zran *zran);
static int zran_index_save_point(struct zran_file *zf, struct point *point);

#define ZRAN_FL_CLOSE 1

static void zran_file_cleanup(struct zran_file *zf, int flags)
{
    TRACE("zran_file_cleanup(%s, %d)\n", zf->filename, flags);

    if (zf->type == INFLATE)
	(void)inflateEnd(&(zf->stream));
    else if (zf->type == DEFLATE)
	(void)deflateEnd(&(zf->stream));

    zf->type = UNUSED;

    if ((flags & ZRAN_FL_CLOSE) && zf->file)
    {
	fclose(zf->file);
	zf->file = NULL;
    }
}

static int zran_inflate_open(struct zran_file *zf, int wbits)
{
    int ret;

    TRACE("zran_inflate_open(%s, %d)\n", zf->filename, wbits);

    if (!zf->file && !(zf->file = fopen(zf->filename, "r")))
	goto err;

    if (fseek(zf->file, 0, SEEK_SET) < 0)
	goto err;

    zran_file_cleanup(zf, 0);

    memset(&(zf->stream), 0, sizeof(z_stream));

    /* allocate inflate state */
    zf->stream.zalloc = Z_NULL;
    zf->stream.zfree = Z_NULL;
    zf->stream.opaque = Z_NULL;
    zf->stream.avail_in = 0;
    zf->stream.next_in = Z_NULL;

    if ((ret = inflateInit2(&(zf->stream), wbits)) != Z_OK)
	goto err;

    zf->type = INFLATE;

    return 1;
err:
    zran_file_cleanup(zf, ZRAN_FL_CLOSE);

    return 0;
}

static int zran_deflate_open(struct zran_file *zf, int level)
{
    int ret;

    TRACE("zran_deflate_open(%s, %d)\n", zf->filename, level);

    if (!zf->file && !(zf->file = fopen(zf->filename, "w")))
	goto err;

    if (fseek(zf->file, 0, SEEK_SET) < 0)
	goto err;

    zran_file_cleanup(zf, 0);

    memset(&(zf->stream), 0, sizeof(z_stream));

    /* allocate deflate state */
    zf->stream.zalloc = Z_NULL;
    zf->stream.zfree = Z_NULL;
    zf->stream.opaque = Z_NULL;

    if ((ret = deflateInit(&(zf->stream), level)) != Z_OK)
	goto err;

    zf->type = DEFLATE;

    return 1;
err:
    zran_file_cleanup(zf, ZRAN_FL_CLOSE);

    return 0;
}

static void zran_index_cleanup(struct zran *zran, int flags)
{
    TRACE("zran_index_cleanup(%s, %d)\n", zran->index.filename, flags);

    if (zran->point)
    {
	free(zran->point);
	zran->point = NULL;
    }

    if (zran->next)
    {
	free(zran->next);
	zran->next = NULL;
    }

    zran_file_cleanup(&(zran->index), flags);
}

static int zran_index_open(struct zran *zran)
{
    TRACE("zran_index_open(%s)\n", zran->index.filename);

    zran_index_cleanup(zran, ZRAN_FL_CLOSE);

    if (!zran_inflate_open(&(zran->index), GZIP_AUTO))
	goto err;

    zran_index_next_point(zran);

    return 1;
err:
    return 0;
}

int zran_index_available(struct zran *zran)
{
    TRACE("zran_index_available(%s)\n", zran->index.filename);

    if (zran->point)
	return 1;

    if (!(zran_index_open(zran)))
	goto err;

    if (!(zran->point))
	goto err;

    return 1;
err:
    return 0;
}

void zran_cleanup(struct zran *zran)
{
    TRACE("zran_cleanup(%p)\n", zran);

    zran_index_cleanup(zran, ZRAN_FL_CLOSE);

    free(zran->index.filename);
    zran->index.filename = NULL;

    zran_file_cleanup(&(zran->data), ZRAN_FL_CLOSE);

    free(zran->data.filename);
    zran->data.filename = NULL;

    free(zran);
}

struct zran *zran_init(char *filename, char *index_filename)
{
    struct zran *zran;

    TRACE("zran_init(%s)\n", filename);

    if (!(zran = malloc(sizeof(struct zran))))
	goto err;

    memset(zran, 0, sizeof(struct zran));
    zran->data.last.offset = -1;
    zran->data.last.point = -1;

    if (!(zran->data.filename = strdup(filename)))
	goto err;

    if (index_filename)
    {
	if (!(zran->index.filename = strdup(index_filename)))
	    goto err;
    }
    else
    {
	if (asprintf(&(zran->index.filename), "%s.idx", filename) < 0)
	    goto err;
    }

    return zran;
err:
    zran_cleanup(zran);
    return NULL;
}

static struct point *zran_index_load_point(struct zran *zran)
{
    int ret;
    struct point *point;

    TRACE("zran_index_load_point(%p)\n", zran);

    if (!(point = malloc(sizeof(struct point))))
	goto err;

    zran->index.stream.next_out = (Bytef *)point;
    zran->index.stream.avail_out = sizeof(struct point);

    /* run inflate() on input until output buffer not full */
    do {
	if (zran->index.stream.avail_in == 0)
	{
	    if (!(zran->index.stream.avail_in = fread(zran->index.buf, 1, sizeof(zran->index.buf), zran->index.file)) || ferror(zran->index.file))
		goto err;

	    zran->index.stream.next_in = (Bytef *)&(zran->index.buf);
	}

	switch (ret = inflate(&(zran->index.stream), Z_NO_FLUSH))
	{
	case Z_OK:
	    break;
	case Z_STREAM_END:
	    if (zran->index.stream.avail_out == 0)
		break;
	default:
	    assert(ret != Z_STREAM_ERROR);  /* state not clobbered */
	    zran_file_cleanup(&(zran->index), 0);
	    goto err;
	}
    } while (zran->index.stream.avail_out != 0);

    return point;
err:
    if (point)
	free(point);
    return NULL;
}

static void zran_index_next_point(struct zran *zran)
{
    TRACE("zran_index_next_point(%p)\n", zran);

    if (!zran->point)
    {
	if (!(zran->point = zran_index_load_point(zran)))
	    return;

	if (!zran->next)
	    zran->next = zran_index_load_point(zran);
    }
    else
    {
	free(zran->point);
	zran->point = zran->next;
	zran->next = zran_index_load_point(zran);
    }
}

static int zran_index_save_point(struct zran_file *zf, struct point *point)
{
    char out[CHUNK];
    unsigned have;
    int ret, flush;

    if (point)
	TRACE("POINT: out=%llu, in=%llu\n", point->out, point->in);

    zf->stream.avail_in = point ? sizeof(struct point) : 0;
    zf->stream.next_in = (Bytef *)point;
    flush = point ? Z_NO_FLUSH : Z_FINISH;

    /* run deflate() on input until output buffer not full, finish
       compression if all of source has been read in */
    do {
	zf->stream.avail_out = CHUNK;
	zf->stream.next_out = (Bytef *)out;
	ret = deflate(&(zf->stream), flush);    /* no bad return value */
	assert(ret != Z_STREAM_ERROR);  /* state not clobbered */
	have = CHUNK - zf->stream.avail_out;
	if (fwrite(out, 1, have, zf->file) != have || ferror(zf->file))
	    goto err;
    } while (zf->stream.avail_out == 0);
    assert(zf->stream.avail_in == 0);     /* all input will be used */

    if (flush == Z_FINISH)
    {
	assert(ret == Z_STREAM_END);	/* stream will be complete */

	/* clean up and return */
	zran_file_cleanup(zf, 0);
    }

    return 1;
err:
    zran_file_cleanup(zf, ZRAN_FL_CLOSE);
    return 0;
}

/* Use the index to read len bytes from offset into buf, return bytes read or
   negative for error (Z_DATA_ERROR or Z_MEM_ERROR).  If data is requested past
   the end of the uncompressed data, then extract() will return a value less
   than len, indicating how much as actually read into buf.  This function
   should not return a data error unless the file was modified since the index
   was generated.  extract() may also return Z_ERRNO if there is an error on
   reading or seeking the input file. */
int zran_extract(struct zran *zran, off_t offset, void *buf, int len)
{
    int ret;
    off_t skip;
    unsigned char discard[WINSIZE];

    /* proceed only if something reasonable to do */
    if (len < 0)
	return -1;

    /* index position needs (?:re)?setting */
    if (!zran->point || (zran->point && zran->point->out > offset))
	zran_index_open(zran);

    if (!zran->point)
	return -1;

    while (zran->next && (zran->next->out <= offset))
	zran_index_next_point(zran);

TRACE("last(offset=%lld,point=%lld) offset=%lld, point=%p(out=%llu) next=%p(out=%llu) len=%ld\n",
    zran->data.last.offset, zran->data.last.point, offset, zran->point, zran->point->out, zran->next, zran->next->out, len);

if (zran->data.last.offset <= offset && zran->data.last.point == zran->point->out)
{
    skip = offset - zran->data.last.offset;
    TRACE("fast-path (skip=%lld)\n", skip);
}
else
{
    TRACE("POINT: in=%llu, out=%llu, bits=%u\n", zran->point->in, zran->point->out, zran->point->bits);

    zran_inflate_open(&(zran->data), RAW_INFLATE);

    if ((ret = fseeko(zran->data.file, zran->point->in - (zran->point->bits ? 1 : 0), SEEK_SET)) < 0)
	goto extract_ret;

    if (zran->point->bits)
    {
	if ((ret = getc(zran->data.file)) == -1)
	{
	    ret = ferror(zran->data.file) ? Z_ERRNO : Z_DATA_ERROR;
	    goto extract_ret;
	}

	(void)inflatePrime(&(zran->data.stream), zran->point->bits, ret >> (8 - zran->point->bits));
    }

    (void)inflateSetDictionary(&(zran->data.stream), zran->point->window, WINSIZE);

    /* skip uncompressed bytes until offset reached, then satisfy request */
    skip = offset - zran->point->out;
    zran->data.stream.avail_in = 0;
}

    zran->data.last.offset = offset+len;
    zran->data.last.point = zran->point->out;

    do {
	/* define where to put uncompressed data, and how much */
	if (skip == 0) {	  /* at offset now */
	    zran->data.stream.avail_out = len;
	    zran->data.stream.next_out = buf;
	    skip = -1;		       /* only do this once */
	}
	if (skip > WINSIZE) {	     /* skip WINSIZE bytes */
	    zran->data.stream.avail_out = WINSIZE;
	    zran->data.stream.next_out = discard;
	    skip -= WINSIZE;
	}
	else if (skip > 0) {	     /* last skip */
	    zran->data.stream.avail_out = (unsigned)skip;
	    zran->data.stream.next_out = discard;
	    skip = 0;
	}

	/* uncompress until avail_out filled, or end of stream */
	do {
	    if (zran->data.stream.avail_in == 0) {
		zran->data.stream.avail_in = fread(zran->data.buf, 1, sizeof(zran->data.buf), zran->data.file);
		if (ferror(zran->data.file)) {
		    ret = Z_ERRNO;
		    goto extract_ret;
		}
		if (zran->data.stream.avail_in == 0) {
		    ret = Z_DATA_ERROR;
		    goto extract_ret;
		}
		zran->data.stream.next_in = zran->data.buf;
	    }
	    ret = inflate(&(zran->data.stream), Z_NO_FLUSH);       /* normal inflate */
	    if (ret == Z_NEED_DICT)
		ret = Z_DATA_ERROR;
	    if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR)
		goto extract_ret;
	    if (ret == Z_STREAM_END)
		break;
	} while (zran->data.stream.avail_out != 0);

	/* if reach end of stream, then don't keep trying to get more */
	if (ret == Z_STREAM_END)
	    break;

	/* do until offset reached and requested data read, or stream ends */
    } while (skip >= 0);

    /* compute number of uncompressed bytes read after offset */
    ret = skip >= 0 ? 0 : len - zran->data.stream.avail_out;

    return ret;

    /* clean up and return bytes read or error */
  extract_ret:
    TRACE("closing on failure\n");
    zran_file_cleanup(&(zran->data), ZRAN_FL_CLOSE);
    return -1;
}

/* Make one entire pass through the compressed stream and build an index, with
   access points about every span bytes of uncompressed output -- span is
   chosen to balance the speed of random access against the memory requirements
   of the list, about 32K bytes per access point.  Note that data after the end
   of the first zlib or gzip stream in the file is ignored.  build_index()
   returns the number of access points on success (>= 1), Z_MEM_ERROR for out
   of memory, Z_DATA_ERROR for an error in the input file, or Z_ERRNO for a
   file read error.  On success, *built points to the resulting index. */
int zran_build_index(struct zran *zran, off_t span, FILE *out)
{
    int ret;
    off_t totin, totout;	/* our own total counters to avoid 4GB limit */
    off_t last;	 /* totout value of last access point */
    unsigned char input[CHUNK];
    unsigned char window[WINSIZE];
    void *ptr;
    int consumed, produced;

    zran_index_cleanup(zran, ZRAN_FL_CLOSE);

    if (!zran_inflate_open(&(zran->data), GZIP_AUTO))
	goto build_index_error;

    if (!zran_deflate_open(&(zran->index), Z_BEST_COMPRESSION))
	goto build_index_error;

    /* inflate the input, maintain a sliding window, and build an index -- this
       also validates the integrity of the compressed data using the check
       information at the end of the gzip or zlib stream */
    totin = totout = last = 0;
    zran->data.stream.avail_out = 0;
    do {
	/* get some compressed data from input file */
	if (!(zran->data.stream.avail_in = fread(input, 1, CHUNK, zran->data.file)) || ferror(zran->data.file))
	{
	    ret = Z_ERRNO;
	    goto build_index_error;
	}

	zran->data.stream.next_in = input;

	/* process all of that, or until end of stream */
	do {
	    /* reset sliding window if necessary */
	    if (zran->data.stream.avail_out == 0)
	    {
		zran->data.stream.avail_out = WINSIZE;
		zran->data.stream.next_out = window;
	    }

	    /* inflate until out of input, output, or at end of block --
	       update the total input and output counters */
	    ptr = zran->data.stream.next_out;
	    produced = zran->data.stream.avail_out;
	    consumed = zran->data.stream.avail_in;
	    ret = inflate(&(zran->data.stream), Z_BLOCK);      /* return at end of block */
	    totin += (consumed -= zran->data.stream.avail_in);
	    totout += (produced -= zran->data.stream.avail_out);

	    if (ret == Z_NEED_DICT)
		ret = Z_DATA_ERROR;
	    if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR)
		goto build_index_error;
	    if (ret == Z_STREAM_END)
		break;

	    if (out && produced)
	    {
		if (fwrite(ptr, 1, produced, out) != produced || ferror(out))
		    goto build_index_error;
	    }

	    /* if at end of block, consider adding an index entry (note that if
	       data_type indicates an end-of-block, then all of the
	       uncompressed data from that block has been delivered, and none
	       of the compressed data after that block has been consumed,
	       except for up to seven bits) -- the totout == 0 provides an
	       entry point after the zlib or gzip header, and assures that the
	       index always has at least one access point; we avoid creating an
	       access point after the last block by checking bit 6 of data_type
	     */
	    if ((zran->data.stream.data_type & 128) && !(zran->data.stream.data_type & 64) &&
		(totout == 0 || totin - last > span))
	    {
		struct point point;

		/* fill in entry and increment how many we have */
		point.bits = zran->data.stream.data_type & 7;
		point.in = totin;
		point.out = totout;
		if (zran->data.stream.avail_out)
		    memcpy(point.window, window + WINSIZE - zran->data.stream.avail_out, zran->data.stream.avail_out);
		if (zran->data.stream.avail_out < WINSIZE)
		    memcpy(point.window + zran->data.stream.avail_out, window, WINSIZE - zran->data.stream.avail_out);

		if (!(zran_index_save_point(&(zran->index), &point)))
		    goto build_index_error;

		last = totin;
	    }
	} while (zran->data.stream.avail_in != 0);
    } while (ret != Z_STREAM_END);

    if (!(zran_index_save_point(&(zran->index), NULL))) /* finish up */
	goto build_index_error;

    zran_file_cleanup(&(zran->index), ZRAN_FL_CLOSE);
    zran_file_cleanup(&(zran->data), ZRAN_FL_CLOSE);

    return 0;

    /* return error */
  build_index_error:
    TRACE("could not build index\n");
    return -1;
}
